1. Field of the Invention
The present invention relates to mesoporous and nanoporous materials and, more particularly, to highly ordered mesoporous materials and the synthesis of the same by using a phosphonated polymer template.
2. Description of the Related Art
In the early 1990's, a family of mesoporous MCM-type (Mobil Corporation) materials was discovered that has a broad range of uses including sensors, catalysis, drug delivery, and solar cells. Depending upon the inorganic material, surfactant templates, and synthetic conditions employed, mesoporous materials with widely varying composition, structure and pore sizes can be synthesized. The first report in 1998 on the synthesis of SBA-type mesoporous materials with very large pore diameter by using triblock copolymer templates was also a significant advance in the field of mesoporous materials chemistry. SBA-type materials allow the immobilization via “host-guest” inclusion processes of larger molecules that are unable to diffuse in the MCM-type mesoporous materials.
The synthesis of well-ordered mesoporous structures requires an extraction step to remove the polymer template molecules. The most common method is calcination, which involves heating the material to a temperature sufficient to oxidize the organic or polymer template. Calcination is widely used in SBA-type materials. Although extraction of polymer templates by calcination can completely remove the templates, the fairly high temperature often causes condensation of surface hydroxyl (—OH) groups on the mesoporous framework and reduction of the number of hydroxyl groups that are often utilized for further organic functionalization of the material. Calcination also modifies the framework, typically by shrinkage, and of course the template, which might otherwise be recycled, is lost.
The second method is solvent-extraction, which is often able to remove ionic templates, but has been less successful in removing non-ionic templates such as tri-block copolymers that are hydrogen-bonded to and occluded in the framework. Other methods include soxhlet extraction, stirring in supercritical fluids and stirring under reflux conditions.
A solar cell is a two-terminal electronic device that delivers electric power to an external load when the cell is illuminated by sunlight, which is the direct source of the electrical power. An important class of solar cells was patented in 1992 by Gratzel and Liska (“Photo-electrochemical cell and process of making same”, U.S. Pat. No. 5,084,365 issued 1992). This cell is based on the use of a porous or mesoporous metal oxide electrode. The device is sensitized to light by attaching dyes and other chromophore molecules to the internal surfaces of the electrode. The complete device is an photo-electrochemical cell incorporating both an electrolyte or polymer that fills the porous material and also a counterelectrode that is in electrical contact with the electrolyte. Because of the common use of dyes as the chromophore molecules, this cell is usually referred to as a “dye-sensitized solar cell” (DSSC). Of particular importance have been mesoporous titanium dioxide electrodes created by sintering of dense titanium dioxide and related microparticles and nanoparticles at temperatures of about 450° C. Intrinsically mesoporous metal oxide materials such as the SBA-type materials noted earlier have also been used because of the greater ordering and control of the pore structure compared to sintered materials. These materials have been prepared starting with solutions of templating polymers that self-assemble into a desired structure, and that serve as the scaffold for the metal oxide. This second class of materials have used a process step of high-temperature calcination to burn off the templating polymer molecules, leaving behind the mesoporous metal oxide material.
Description of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section (as well as throughout the application), these discussions should not be taken as an admission that the discussed publications are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section (as well as throughout the application), they are all hereby incorporated by reference into this document in their respective entirety(ies).